Ultra-high molecular weight polyethylene - UHMWPE behaviour in injection molding processes

Abstract

[EN] Polyethylene UHMWPE is a semi-crystalline thermoplastic polymer. UHMWPE polyethylene structure consists of ordered regions (as sets of crystalline lamellae) embedded in a disordered amorphous phase. In production and research, five categories of polyethylene are found: very low density VLDPE, linear low density LLDPE, low density LDPE, high density HDPE and ultra high molecular weight UHMWPE. UHMWPE polyethylene has a relative molecular mass Mr (usually within 2-6 x106 g/mol, with an average minimum 3.1 x106), superior to the HDPE polyethylene (values ranging from 50.000 to 300.000 g / mol). In the last 40 years, the polyethylene UHMWPE is widely used for the manufacture of implants, especially for load-bearing applications such as the acetabular cup of total hip and the tibial plateau. In this medical application, polyethylene UHMWPE has relative molecular mass of (4 to 6) x 106 Mr. In polyethylene processing through ram extrusion, compression moulding, injection moulding etc, the viscosity in the polymeric system gets considerably high once the molecular weight increases. In this situation, the polyethylene processing (in pure state)by moulding injection, raises major difficulties. Given this, the present paper analyses the UHMWPE polyethylene behaviour in the injection process using the Moldflow program. The modelling and the simulation of the injection process were effectuated for the acetabular cup manufacture.